Closed loop fuel control system



NOV 8, 1965 F. E. SCHEIDLER 3,283,499

CLOSED LOOP FUEL CONTROL SYSTEM Filed Oct. 24, 1965 4 Sheets sheet l F/G, M

/Z AZZ V J/ iig? @E D NOV- 8, 1966 F. E. scHExDLER 3,283,499

CLOSED LOOP FUEL CONTROL SYSTEM Filed Oct. 24, 1963 4 Sheets-Sheet 2 flip l massa/QE 4 Sheets-Sheet I5 F. E. SCHEIDLER CLOSED LOOP FUEL CONTROL SYSTEM Nov. 8, 1966 Filed oct. 24, 1965 AIWWH www,

d W 5 M J a Nov. 8, 1966 F. E. scHElDLER 3,283,499

CLOSED LOOP FUEL CONTROL SYSTEM Filed Oct. 24, 1963 4 Sheets-Sheet 4 United States Patent O 3,283,499 CLOSED LOOP FUEL CONTROL SYSTEM Frederick E. Scheidler, West Hartford, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Oct. 24, 1963, Ser. No. 318,671 Claims. (Cl. 60-39.28)

This invention relates to fue-l controls and particularly to fuel controls for controlling turbine-types of power plants.

Specifically, this invention relates to fuel control mechanism, inc-luding the computing and metering devices that execute the principles disclosed and claimed in a patent application Serial No. 314,755 recently tiled by L. A. Urban October 8, 1963, and assigned to the same assignee and issued into Patent No. 3,242,673.

In the aforementioned application lit was pointed out that the heretofore known fuel -control schedules fuel flow to the engine as a function of measured engine operating parameters and that this schedule is built into the control by the use of cams, levers, links and the like in order to insure that the fuel ow is compatible with desired engine operations. Before designing these heretofore controls, it was pointed out that it was necessary to know the heat content of the fuel because it was the ultimate function of the control to develop a given quantity of B.t.u.s for a given operating condition.

In these heretofore known fuel controls the scheduling of the fuel in accordance wi-th preselected engine operating parameters, the principles employed were based on an open-loop control concept. This concept resulted in the development of a group of fuel controls that utilized a built-in parameter of Wf/Pg, where Wf is fuel ow in pounds per hour and P3 is the pressure value of the gases discharging from the compressor.

Basically, the well-known method of scheduling provided by these heretofore known controls would be to sense the actual compressor disch-arge pressure and multiply this value by the computed Wf/P3 parameter to position the metering valve or valves of the fuel control. In these controls it was a general practice to compute the Wf/P3 parameter as a function of compressor speed and compressor inlet temperature for acceleration and steadystate engine operations, while other parameters could also be employed depending on the sophistication desired.

Because of the advent of the regenerative type of engine where an unknown quantity of heat is added to the combustion section and because of the desirability of utilizing different types of fuel for the same fuel control, the type of heretofore fuel control described above proved unsatisfactory.

This led to the departure of the Wf/P3 parameter type of control and resulted in the invention disclosed and claimed in the aforementioned Urban application.

Accordingly, an object of this invention is to provide a fuel control as described embodying `structure that controls fuel flow to the engine wherein the parameter APb/P3 is utilized as the primary control parameter, where APb represents the pressure drop across the burner in the case of a nonregenerator type of engine and the pressure drop across the combined regenerator and burner in la regenerator type of engine and P3 represents the compressor discharge pressure.

A still further object of this invention is to provide a fuel control having a hydraulic computing system for positioning a fuel regulating valve of the integrating type to provide a closed-loop control system.

A still further object of this invention is -to provide in a fuel control as described a hydraulic computing system that compu-tes a function of speed of the compressor, a

3,283,499 Patented Nov. 8, 1966 function of power lever position, `a function of compressor discharge pressure in terms of desired APb and compute actual APb so that the fuel metering system meters perature) `and a function of the position power levers designed for a solid shaft type of jet engine to a free turbine type of jet engine.

A still further object is to provide in a fuel control as described, mechanism for defining steady-state engine operations wherein a function of P3, Ng and power lever position is converted in ter-ms equivalent to the desired AP still further object of this invention is to provide in a fuel control as described mechanism for defining acceleration engine operation wherein a function of P3, Ng and T2 is converted in terms equivalen-t to the desired AP still further object of this invention is to provide for a fuel -control as described a hydraulic computing system that computes surge and temperature of the gases at the inlet of the turbine independently and permits the higher value of the two to control the fuel metermg system.

A still further object of lthis invention is to provide mechanism for a fuel control `as described which is characterized .as being readily economical to manufacture,

relatively s imple, yet accurate and reliable while subjected to lrugged use.

A still further object of this invention is to provide 1n a fuel control as described, mechanism for obtaining theoretically correct steady-state engine operation and Y acceleration limiting of the engine as opposed to some heretofore fuel controls which merely provide approximate steady-state engine operation and approximate acceleration limits.

Other features and advantages will be apparent from i the specification and claims and from the accompanying drawings which illustrate an embodiment of the 1nvention.

FIG. l is a schematic illustrating a fuel control controlling a regenerative type of jet engine of the solid shaft type.

FIG. 2 is a schematic illustration showing a fuel control utilizing the concept of this invention.

FIG. 3 is a graphical illustration showing a typical operating condition of the fuel control.

FIG. 4 is a graphical illustration of the acceleration limit as scheduled by the fuel control.

FIG. 5 is a block diagram schematically illustrating the basic concept of this invention.

FIG. 6 is a partial schematic showing a suitable pres- V sure regulating and fuel flow shut off system readily j the incoming air to the burner in indirect heat exchange with the air discharging from the turbine. For this purpose, passage 22 admits compressor discharge air into heat exchanger 20 and delivers it to the burners through line 24 while passage 26 admits turbine discharge air into heat exchanger 20 and discharges it through passage 28 to ambient;

The fuel control generally illustrated by numeral 30 serves to meter fuel being pressurized by pump 32 to burner section 14 through line 34. Manifold drain line 261, absolute pressure control 260 and drain line 36 serve to return fuel from the fuel control to the inlet of pump 32. `As will be more fully illustrated hereinafter, the fuel control receives several signals from the parameters selected to compute the desired amount of fuel necessary to obtain optimum operation. For this purpose, the fuel'control senses the compressor inlet temperature as illustrated via sensing line 38, compressor discharge pressure via line 40, burner discharge pressure via line 42, and r.p.m. of the compressor via line 43 and the position of power lever 47 via shaft indicated by line 44. It is to be understood that the power lever is mounted somewhere available to the operatorvof the aircraft and the terminology power lever is not particularly limited to a particular lever in the cockpit of the aircraft. Rather it is intended to cover any linkage connecting the cockpit to the fuel control whether it be referred to as a go handle, power lever or throttle lever or the like. Furthermore, it is to be understood that the use of regenerative types of turbine type of engines is shown merely for illustrative purposes and is not to be construed as being limited thereto. As Will be obvious to one skilled in the art, this concept is equally applicable to control straight jets, turboprop jets, regenerative types of jet engines whether it is of the solid spool, twin spool, or the free turbine type of engine. It will be appreciated that for a regenerator type of power plant it is preferred to sense the pressure upstream of the regenerator and downstream of the burner to obtain the burner pressure drop signals or Pta and PS3 to measure (Pta-Ps3) P 3 valve generally indicated by numeral 50 through line 33 where it is metered to the engine via passage 34. (It will be understood that like numerals reference like parts in the various drawings.) Throttle valve 50 comprises spool 52 having its ends 54 and 56 subjected to metered pressures for positioning the spool in cylinder 58. Metering edge 60 of spool 52 cooperates with port 64 for establishing the proper area for metering the required amount of fuel to the engine. The maximum travel of spool 52 is governed by adjustable stop 62 which serves to define the minimum opening of port 64 for establishing the minimum fuel ow to the engine.

In this preferred embodiment it is not deemed absolutely necessary to maintain the pressure drop across the throttle valve at a constant Value. However, if the requirement of the fuel control necessitates a minimum fuel flow, it then becomes necessary to maintain the pressure dropacross the throttle valve at a constant value. I have shown in FIG. 6 suitable pressure regulating mechanism adapted for the purpose of maintaining the pressure drop across the throttle valve at a constant value.

Reference is made to FIG. 6 wherein the pressure regulator generally .indicated by numeral 400 comprising Valve members 402 having end 404 responsive to hydraulic pressure evidenced upstream of throttle valve 50 and end 406 responsive to hydraulic pressure evidenced downstream of throttle valve 50. For this purpose line 408 leads uid into chamber 410 and line 412 leads fluid in chamber 414. Spring 416 acts on end 406 and urges the valve toward the closed position.

It will be apparent from the foregoing that the position of valve member 402 is determined by the difference between the forces created by the pressure acting over ends 404 and 406 and the force created by the spring. The force of the spring, therefore, establishes the pressure drop across the throttle valve. This force may be adjusted by the adjusting mechanism 416.

To maintain the value of the pressure drop across throttle valve constant, valve member 402 is positioned to meter fluid from line 418 to line 420. Lines 418 and 420 lead uid to bypass the throttle valve back to the reservoir. It is desirable that the pressure of the fuel used in the control computing section does not become less than a specified minimum value to assure satisfactory operation of the computing valves. Further, it is desirable to shut off the ow of fuel to shut down the engine, particularly during a malfunction. For this purpose valve 422 is employed. This valve comprises valve member 424 urged by spring 426 to the closed position.k The underside of valve member 424 is subjected to the pressure of the metered fuel. When the pressure creates a force larger than the combined forcelof spring 426 and drain pressure acting on the opposite sidey of valve member 424, the valve moves open.

To close valve 422, solenoid valve 430' is disposed in line 432 normally conducting fluid fnom chamber 423 -t-o drain, switch 436 is depressed Iby the pilot for interconnecting lines 438 and 432. This leads uid upstream of throttle valve 50 into chamber 434 to act on the right end of valve member 424 to urge the valve member to'close and 'hence starving -the engine from fuel. It will be appreciated that the value of pressure upstream of throttle valve is always at a higher value than `the Value of the pressure downstream thereof.

In order to more fully understand this invention, the

B represents an infinite number of ydroop governor lines` which are characteristic of the operation of the governor, curve C represents the corrected temperature of the engine (T 4/ T2) and curve D represents surge. Assume for illustration purposes that it is. desired to control the engine at point lE which falls on the steady-state line at the point where line B intersects line A and assuming that this is at 50% of the desired speed of the compressor. To obtain this value, pilot lever 46 is rotated to position valve 88 which varies the area of orifices 90 and 92 for dumping fluid out of lines 94 and 96 and establishing a pressure therein equivalen-t to the power -desired when the pressure in passage 100 `corresponds to 50% actual compressor speed. Setting the area of orifices and 92 serves to control the pressure ratio between thepressure in passages and 95 disposed upstream and ldownstream of orifice 98 respectively. From the foregoing, it is apparent that the pressure evidenced between orifice 98 and orifices 90 and 92 is a function of the displacement or position of throttle lever 46 and the pressure in passage 100, and essentially is the speed signal atwhich the compressor is desired to rotate.

The governor generally indicated by numeral 102 serves to measure -the speed of the compressor and produce a signal indicative of the actual speed of the compressor. Governor 102 contains rotating platform 104 carrying a pair of flyweights 106 pivotally mounted on upstanding` members 103, each of which contain 4arms 108 bearing against spool 110 of speed control valve 112..,Theforce created by the flyweights is a function of speed squared.

This valve serves to meter high pressure fluid issuing from line 114 into passage 100 via port 118and branch line 116, and -the metering edge of spool 110 establishes an area for metering high pressure uid into port 118 for producing a pressure i-n line 116 to be equivalent to a function of -the square of the speed of the compressor. Fluid leaking around spool 110' seeks to the upper side thereof to counteract the force created by the flyweights. The ymetering edge of spool 110 .may be considered as a variable area orifice and its variation in area controls and establishes the pressure drop across itself to create a pressure in passage 100 which when applied to the upperside of spool 110 balances the fiyweight force. Hence, i-t is apparent that the pressure acting on the underside of pilot valve 122 is a function -of actual speed land power lever position which is speed error.

Still referring to FIG. 2 it will be further noted that compressor discharge pressure is sensed lby compressor discharge sensor generally indicated by numeral 130 which comprises bellows 132 and control valve 134. Compressor discharge pressure transmitted via line 41 is admitted internally of bellows 132 which is surrounded by hydraulic fluid. The free end of the bellows abuts against the end of control valve 134 to position it as a function of the value of the compressor discharge pressure. Hence, the pressure in passage 136 is established .to be a function of compressor discharge pressure. This is accomplished by metering pressure from the high supply pressure line 138 through valve 134 into lines 139 and 140 connected to chamber 142. Valve 134 displaces until the pressure in chamber 14-2 is equal to the pressure internally of the bellows. When valve 134 is in its balanced position, that is, when it no longer continues -to travel, the pressure in chamber 142 and hence line 136 has been established. It will be noted that the under end of valve 134 is counteracted by the pressure equivalent to the pressure in chamber 142 by the interconnection made via lines 139 'and 140. This assures that the pressure established by valve 134 is solely a function of a compressor discharge pressure.

The metering land of valve 122 cooperating with port 150 is designed so that its area is a function of the scheduled pressure drop across the burner divided by the compressor discharge pressure. By virtue of the relationship of oce 150 with respect to orice 152 which is disposed in line 154 leading fluid to drain, a multiplication is effectuated which results in a pressure in passage 156 which is a function of the produc-t of the pressure in passage 136 and the ratio of orifice areas 150 to 152. Hence, compressor discharge pressure component is multiplied out so that pressure in line 156 is now in terms of the desired pressure drop across the burner which has been established as a function of speed of the compressor, pilot lever position and compressor discharge pressure.

This pressure is fed into cylinder 58 to act on end 54 of spool 52 of the throttle valve. This pressure counteracts the force created by the pressure on end `56 of the throttle valve and the throttle valve being of the integrating type, spool 52 translates at a constant velocity which is a function of the magnitude of the error between the two pressures. This causes flow to be metered through the throttle valve to the engine until the pressures on either end of spool 52 are balanced. When this occurs, the entgine will be operating at point E as shown in FIG. 3.

Now returning back to FIG. 2, hydraulic pressure, whose value is proportional to the actual pressure drop across the burner, is admitted into cy-linder 58 to `act on end 56 of spool 52. This pressure is established by the 'burner pressure drop sensor generally indicated by numeral 66 which comprises bellows 68 having its free end suitably connected to lever 70. Pressure through line 40 is admitted internally of bellows 68 -and pressure through sensing line 42 is admitted to act externally over bellows 68. Obviously, the force on lever`70 will be indicative of the diffe-rence between the two pressures so that the signal produced by the movement of lever 70 is proportional to the pressure drop across the burner. The free end of lever 70 acts against pilot valve 72 by virtue of its rotational movement about pivot 71 posed in drain line 78. Hence, the relationship between land and port 74 of valve 72 denes an area for admitting uid from supply line 82 which receives fluid from line 136 into passage 84. This cooperation is such that the pressure in line 84 acting on end 56 or spool 52 is a function of the actual pressure drop across the burners.

Now that the steady-state operation ofthe control has been described, the next portion `of the specication will be concerned with describing the acceleration schedule of the control which permits the throttle valve to regulate fuel to the engine while preventing the engine from becoming overheated and preventing the compressor from operating in the surge regi-on. This is illustrated in FIG. i

3 by curves C and D respectively.

Still referring to FIG. 2, it will be noted that fluid in line 136 is directed to the valve generally indicated by numeral 200 via line 201, which pressure has been established by the compressor discharge pressure sensor 130. Valve 200 comprises spool 202 subjected to the forces of spring 204 acting on one of its ends and a controlled pressure acting on the opposing end. Metering edge 206 on spool 202 is so ydesigned that it meters fluid discharging from valve 200 into line 208 so that the pressure in line -V 208 is a function of the scheduled surge limiting value of the pressure drop across the burner. `fully explained hereinafter, the pressure creating the force acting on one side of spool 202 is a function of corrected w place in a manner similar to that described in connection with valve 122. This multiplication, in essence, is

a multiplication of the burner pressure drop divided by compressor discharge pressure times compressor discharge pressure, thus canceling out the compressor Y discharge pressure term so that the pressure between restriction 210 and the metering land 206 is solely a function of scheduled burner pressure drop. Its value is the p-oint where surge would ensue if the ratio of the burner pressure to compressor discharge pressure goes below a predetermined value; namely, that shown as-curve D as shown in FIGURE 3. Hence, if the pressure should go below line D when operating within a specific speed range, surge would ensue.

It will be noted from the drawing that the uid in line 1 208 is directed via line 209 to temperature-surge-selector valve 212 and the `'acceleration-governor-selector valve 214. In the position as shown in FIG. 2, the temperature-surge-selector valve 212 is placed in the extreme right position. This is due to the fact that the pressure on the left-hand end is at a higher value than the pressure on the right-hand end. In this position, line 216 communicates with lines 209 and 218 for directing this pressure to act on the left-hand end of acceleration-governor-selector Y Since the right-hand end of accelerationgovernor-selector valve 214 is subjected to the pressure in valve 214.

line 156, 'which as described above, is a function of the scheduled burner pressure drop, which, in turn, is a func tion of the ratio of burner pressure drop to compressor discharge pressure, it will shift to the right if the burner pressure drop goes below line D (see FIG. 3). Hence,

if the force created by the pressure generated by valve 200 evidenced on the left-hand end of acceleration-governor-selector valve 214 increases -over the force acting in an opposing direction, the valve will shift to the right connecting lines 220 and 222 with line 218 for applying that pressure on end 54 of throttle valve 50. This has the effect of urging spool 52 of throttle valve 50 in a down- I' As will be more Metering land 206 is ldesigned l ward direction to prevent the weight flow of fuel to the engine from exceeding a value which would cause the engine to surge and hence, maintain the operation of the engine above line D which is the urge limit of engine operation.

Control valves 200 and 240 cooperate to assure that the engine does not go above a maximum temperature. Control valve 200 meters compressor discharge pressure fluid through line 230 into line 232. The contour of metering edge 234 of spool 202 is designed Vso that it defines an area of cooperating metering port as a function of burner pressure drop divided by compressor discharge pressure and compressor inlet temperature raised to some power. As was mentioned in connection with the operation of the metering edge 206 in connection with the fixed restriction 210, the operation of metering edge 234 in connection with restriction 236 disposed in drain line 237 is such th-at the value of the pressure in line 232 is the product of the multiplication between the pressure of line 230 which is a function of compressor discharge pressure and the function -of the area of the metering edge 234. This multiplication produces a pressure in line 232 equal to a function of the pressure drop across the burner times the temperature at the inlet of the burner raised to some power.

Control valve 240 serves to place the pressure in line 238 in terms compatible with the term used in controlling the throttle valve 50. Schematically illustrated, valve 240 responds to the position of bellows 242 which is acted on by compressor inlet temperature air and produces a signal whose value is equivalent to the temperature at the inlet of the compressor. This signal then translates spool 241 of valve 240 for controlling the area created by metering edge 244. This area is made to vary as a function of the reciprocal of the temperature of the inlet of the compressor raised to some power. lts relationship with the fixed restriction 248 disposed in drain line 249 which is similar to the relationship described in connection with the area established by metering edge 206 and restriction 210 produces a multiplication between the terms represented by the pressure in line 232 and the term introduced by metering edge 244. Hence, the factor of temperature represented by the pressure in line 232 is canceled out in line 238 so that the pressure in line 238 becomes solely a function of the pressure drop across the burner. Since this pressure acts on the righthand end of temperature-surgeselector valve 212, it will cause the valve to shift to the left interconnecting line 238 and line 218 to cause this pressure to act on the lefthand end of acceleration-governor-selector valve 214 when it exceeds the pressure acting on the left-hand end. In essence, then, if the temperature should exceed the value represented by curve C of FIG. 3, the pressure on the left-hand end of acceleration-governor-selector valve will exceed the pressure acting on the right-hand end, causing the valve to shift to the right interconnecting lines 218 and 222 and chamber 58 subjecting end 54 of throttle va1ve'50 to that pressure. This pressure prevents throttle valve from metering a fuel liow which would result in overtemperaturing the engine by maintaining system operation above curve C on FIG. 3.

Curve C is a line of constant corrected turbine inlet temperature and for a specified value of inlet temperature describes a specific turbine inlet temperature limit. The control system described herein utilizes a mathematical expression which defines a relationship between a specific value of turbine inlet temperature and burner pressure drop divided by burner pressure multiplied by compressor inlet temperature raised to a power at a specified value of corrected speed. Hence, for each value of corrected speed, a constant turbine inlet temperature can be described as a function of burner pressure drop divided by burner pressure and compressor inlet temperature raised to a power as illustrated in FIG. 4. As can be seen from FIG. 4, curve M represents the surge limit and the area defined under the curve represents the surge region, ie., where surging of the compressor would ensue. Curve N represents the temperature limit and the area defined under this curve represents the overtemperature region.

The pressure acting on the right-hand en'd of spool 202 of valve 200 is established by valve 240 and governor 102 which, as indiated above, positions the spool as a function of temperature at the inlet of the compressor and speed of the compressor. Metering edge 250 of valve spool 241 cooperates with port 252 defining an area equal to a function of the temperature of the inlet of the compressor. The opening thereof bleeds pressure from line to drain via line 254 for controlling the pressure drop across restriction 120. This has the effect of establishing a pressure downstream of restriction to be equivalent to a value which is a function of speed squared divided by the temperature of the inlet of the compressor. The combined effect of valves 200 and 240 establishes a maximum temperature line and relates this temperature limit in terms compatible with the terms controlling the throttle valve; namely, making that pressure equivalent to a function of the scheduled value of the pressure drop across the burner.

Since it -is desirable to compute the terms of the parameters in their absolute values rather than gauge pressure values, absolute pressure control 260 is employed. This control is located in the drain line (all the drain lines indicated by P0 in the drawings) for controlling the drain pressure of all the control valves to equal the absolute value established by evacuator bellows 262. Bellows 262 acts against spool 264 which is counterbalanced by drain pressure admitted into chamber 266 via line 267. It will be appreciated that the various drain lines lead drain fluid back to the input of the pump (see FIG. l). Pressure control 260 is located in the drain manifold line 261 and serves to meter drain fluid into drain line 36. This establishes a datum line equivalent to an absolute value so that the pressure control values use la zero pressure datum rather than a gauge pressure datum.

In summary, therefore, the control assures operation of the engine as shown in the graph of FIG. 3. For steadystate operation, the pilot lever 46 establishes the desired power by producing a signal which is converted into a. pressure value. This signal Ican be considered as the desired speed of the compressor. Governor 102 serves to measure actual speed and convert it to a pressure signal which is equal to a function of the square of compressor speed. Both of these pressure signals are mixed and the resultant pressure is sensed by valve 122. The change in this pressure from a set point is equivalent to the error between actual speed and desired speed.

Valve 122, then converts this signal in terms of the control parameter APb/P3 by varying the area of its metering orifice as a AP), f( P3 Actual P3 is measured by 'control 130 and produces a pressure equal to a (P3) which is applied to the metering orifice of valve 122. Here the functions are multiplied so that the output of valve 122 is a uid pressure whose value is a f(APb).

This value represents the ratio APb/P3 of the control parameter, but is in a simplified term expressing the scheduled power (by virtue of power lever position, speed and compressor discharge pressure) at which the engine is desired to operated.

The actual burner pressure drop is measured by lcontrol 66 and converts its signal to a fluid pressure which is a f(APb). This represents the actual pressure drop across the burner. It will be noted that the term f(APb) obtained by the power lever, compressor discharge pressure sensor, and governor represents the scheduled pressure drop across the burner. The integrating throttle valve senses the difference between both values and changes fuel ow to the engine until both pressures have been balanced which is at the steady-state ope-ration point.

The acceleration schedule is designed to allow fuel to be metered to the engine at its highest flow capacity but yet preventing the temperature to increase beyond the structural limits of the engines component parts and preventing the compressor from operating within the surge region. This is represented in FIG. 3 by curves C and D. It will be noted that the present fuel control computes both the temperature limit T4 and surge limit and allows the Vhigher of the two signals to control. That is to say, that the two values (temperature and surge) `are computed in terms of the control parameter and the higher Arb/P3 of the two controls.

To compute the surge schedule, pressure equivalent to a MP3) as generated by `control 130 is fed to valve 200 which generates the f(APb) surge signal. This is accomplished by designing the Ametering land to vary its area as a f P3 surge. The valve multiplies this function by f(AP3) to produce the KAPD) surge pressure value. The position of this valve is varied as :a #N2/T2) which is established by governor 102 and valve 240. It will be noted that the f(N2/T2) is the abscissa of the chart shown in FIG. 3.

Hence, it is apparent from the foregoing that valve 200 produces a pressure which is a function of the control parameter APb/Pa and N/ \/`2 so that the curve D can be defined in control functions.

The overtemperature is limited in accordance with curve C of FIG. 3 by valves 240 and 200. It will be noted that curve C represents turbine inlet temperature corrected by compressor inlet temperature, T4/T3. The curve shown in FIG. 4 illustrates the relationship utilized by this control system.

To this end, the -schedule for overtemperature is governed by valve 200 which is positioned as f(N2/T2 representing the abscissa of the graph in FIG. 4. (Note the plot of the graph is in terms of N VTZ which is merely a dierent expression for the same equation.) The metering land of spool 202 of valve 200 defines an area of its metering port to be a Pb x f in@ l which establishes the desired turbine inlet temperature limit. This valve also multiplies the pressure signal f(P3) by this function to produce a pressure value equal to a f(APbT2X).

The area of the orifice defined by metering land 244 of valve 240 varies as a and this valve serves to multiply this function by f(APbT2X) This produces a pressure signal in terms compatible with the terms of the pressure signal applied to the throttle valve; namely, f(APb).

Valve 212 then senses both the surge signal and the overtemperature signal and directs pressurized fluid equivalent to the function of the higher value to valve 214. Valve 214 then senses this signal and compares it with the desired steady-state signal and directs the greater of the two to throttle valve 50. In this manner, the limits to prevent surge and overtemperature are provided, and the acceleration schedule is established.

Operation The operation of the fuel control is best described by referring to FIG. 3, assuming that the fuel control is put in the on-condition from the off-condition. The pilot rotating the power lever establishes a signal desire-d to produce the desired thrust or horsepower required for the particular aircraft manuever. This sets the governor and the ratio APb/P3 to operate at theprescribed condition. v Assume that power is desired for the steady-state operation as represented by point F intersecting the droop governor line B at steady-state line A.

The power lever control has the effect of generating a signal to the throttle valve to call for maximum fuel lioW l,

so that the engine operation at this point is defined by line G. Throttle valve 50 will translate in a direction to increase quantity of fuel to the engine until line G approaches curve C. The temperature limit of the acceleration schedule then takes over and schedules fuel iiow which results in operation along line H. As the speed of the compressor increases, fuel flow is scheduled by the droop line B, the governor takes over control of the throttle valve to reduce fuel tiow along droop line B until the engine operations lhave .reached point F.

While FIG. 2 illustrates schematically mechanism for providing a fuel control for accomplishing the schedule shown in FIG. 3, it will be obvious to one skilled in this art that this merely represents one way of executing the basic concept. For clarification, FIG. 5 is included herein to show fundamentally the execution of the concept of utilizing APb/P3 as the primary control parameter.

Referring now generally to the block diagram shown in FIG. 5, it Will be noted that the position of the power lever is indicated by the symbol X2 and the other symbols represent terms already designated herein above. 6X2 is fed into block 300 where it is computed in terms of Ng/X2 where merely represents the rate of change.

The output is fed to block 302 where -it is compared with the actual Ng for producing an error output signal.

Block 304 then computes this term in the form and transmits it to selector block 306. The selector serves to transmit the lower or higher value of one of several signals fed thereto for transmitting it to the next summation junction. This junction is represented by block 308 which responds to actual Pg/APb. The two signals are `compared and the difference (Pa/APb) error i s` transmitted to block 310. Block 310 represents mechanism for converting this signal into terms of fuel flow compatible with the amount established by the fuel control. As noted in the drawing, symbol S represents a La Place transform function representing the integration of grator for positioning the throttle valve for controlling A the fuel ow.

Block 314 illustrates mechanism serving to establish the minimum fuel ow. v i In order to establish the control pressure, it was necessary in several instances to perform a multiplication. The multiplication in each of these instanceswas accomplished by varying the area of an orifice designed to vary at a predetermined function. For example, in the instance where the control computed a speed error signal in terms of f(APb), valve 122 multiplied the pressure l 1 whose value was established as f(P3) times the area of the metering land which was established as APb f( P3 This may be shown as follows:

Consider fthat orifice 150 (A150) is in series with restrictor 152 (A152) and Pu is the pressure upstream of A150; P1 is the pressure intermediate A150 and A152; Pd is the pressure downstream of A152; vand A is a symbol representing :the area of the particular orifice. It is well known that:

. Q=KA\/TP Where: Q=volume flow through orifice K=some design constant A Le area AP=pressure drop across an orifice then Qo=KA15o\/Pu-Pi and Q152=KA152VP1Pd however y Q15o=Q152 then A m: Pu-Pi A150 Pi Pd multiplying out the square root, then (A152)2 Pu-Pi {Amay-Pi-Pd and adding to the expression (Pd-Pd) (Anagni-Pi) +de-Pd) c (Amr Pi-Pd by factoring l AP 1HAI-52Wmaufdesred KE) since Pu-P0=(P3). therefore, pressure in line 156=f(APb).

therefore, pressure in line 1S6=f(APb).

Preferably, the various computing andvmetering valves of this fuel control should be of the continuously rotating type in order to keep the frictional yeffect to a minimum. Rotating valves are not new and a detailed description thereof is omitted herein for the sake of simplicity and convenience.

What has been shown by this invention is a mechanism of a fuel control for any gas turbine engine utilizing a pressure drop across the heat additive mechanism of the.

i2 engine or the differential between the static and total pressure of the working fluid divided by the compressor discharge pressure as a primary control parameter. The mechanism provides an accurate and reliable control Which is characterized as being relatively simple to manufacture, relatively economical yet capable of rugged use.

It should be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the spirit or scope of this novel concept.

I claim:

1. A fuel control for controlling a gas turbine power plant having a burner, a turbine receiving the products of combustion discharging from said Iburner and a compressor driven by said turbine, said control having a hydraulic computing system including first valve means movable in response to compressor discharge pressure for generating a first hydraulic pressure signal, second valve means having connecting means communicating with said first valve means for receiving said first hydraulic pressure signal and being movable in response to corrected compressor speed for generating a second hydraulic pressure signal, third valve mean having connecting means communicating with said second valve means for receiving said second hydraulic pressure signal and being movable in response to compressor inlet temperature for generating a third hydraulic pressure signal, said control also having a fuel metering system including fuel regulating means having actuating means for injecting fuel to said burner, means for applying said third hydraulic pressure signal to said actuating means, means responsive to the pressure drop across said burner for developing a fourth hydraulic pressure signal, and means for applying said fourth hydraulic pressure signal to said actuating means, whereby the said actuating means will position said fuel regulating means in response to the difference between said third hydraulic pressure signal and said fourth hydraulic pressure signal.

2. A fuel control as defined in claim 1 wherein said fuel regulating means includes a movable valve having a metering port, said valve movable at a velocity which is a function of the magnitude of the difference between said third hydraulic pressure signal and said fourth hydraulic pressure signal.

3. A fuel control for controlling a gas turbine power plant having a burner, a turbine receiving the products of combustion discharging from said burner and the compressor driven by said turbine, said control having a hydraulic computing system including first valve means responsive to compressor discharge pressure for generating a first hydraulic pressure signal proportional to compressor discharge pressure, second valve means having first and second metering means and a pair of parallel disposed fluid connections interconnecting the first and second metering means and said first valve means and being responsive to corrected compressor speed, third valve means having connecting means communicating with first -metering means and being responsive to compressor inlet temperature, a selector valve having fiuid connecting means communicating with the third valve and said second metering means, said control also having a fuel metering system including fuel regulating means for injecting fuel to said burner, fourth valve means responsive to the pressure drop across said burner for developing a hydraulic pressure signal proportional to the pressure drop across the burner, said fuel regulating means being movable in response to the difference between said hydraulic pressure signal proportional to the pressure drop across the burner and the higher of the pressures applied to said selector valve. i

4. A fuel control as claimed in claim 3 wherein said hydraulic computing system includes a drain, passage means connected to the connecting means of said third valve communicating with said drain, and a restrictor in said passage means intermediate drain and said connecting means of said third valve.

13 5. A fuel control as claimed in claim 4 wherein said hydraulic computing system includes another passage means communicating with the uid connecting means of said selector valve, and a restrictor in said passage means intermediate drain and said fluid connecting means of said selector valve.

References Cited by the Examiner UNITED STATES PATENTS 2,592,385 4/1952 Borden. 2,740,295 4/ 1956 Perchonak 60-39.28 X 2,792,685 5/ 1957 Constantino 60-39.28

10/1957 Arkawy 60-39.28 10/1958 Wright 60-39.28 X 2/1961 Sims 60-3928 3/1961 Flanigan et al 60-39.28 4/ 1961 Zeisloft 60-39.28 5/1961 Embree 60-39.28

OTHER REFERENCES Sobey: Control of Aircraft and Missile Powerplants;

received in Patent Oce, July 29, 1963, page 11 relied on.

JULIUS E. WEST, Primaly Examiner. 

1. A FUEL CONTROL FOR CONTROLLING A GAS TURBINE POWER PLANT HAVING A BURNER, A TURBINE RECEIVING THE PRODUCTS OF COMBUSTION DISCHARGING FROM SAID BURNER AND A COMPRESSOR DRIVEN BY SAID TURBINE, SAID CONTROL HAVING A HYDRAULIC COMPUTING SYSTEM INCLUDING FIRST VALVE MEANS MOVABLE IN RESPONSE TO COMPRESSOR DISCHARGE PRESSURE FOR GENERTING A FIRST HYDRAULIC PRESSURE SIGNAL, SECOND VALVE MEANS HAVING CONNECTION MEANS COMMUNICATING WITH SAID FIRST VALVE MEANS FOR RECEIVING SAID FIRST HYDRAULIC PRESSURE SIGNAL AND BEING MOVABLE IN RESPONSE TO CORRECTED COMPRESSOR SPEED FOR GENERATING A SECOND HYDRAULIC PRESSURE SIGNAL, THIRD VALVE MEANS HAVING CONNECTING MEANS COMMUNICATING WITH SAID SECOND VALVE MEANS FOR RECEIVING SAID SECOND HYDRAULIC PRESSURE SIGNAL AND BEING MOVABLE IN RESPONSE TO COMPRESSOR INLET TEMPERATURE FOR GENERATING A THIRD HYDRAULIC PRESSURE SIGNAL, SAID CONTROL ALSO HAVING A FUEL METERING SYSTEM INCLUDING FUEL REGULATING MEANS HAVING ACTUATING MEANS FOR INJECTING FUEL TO SAID BURNER, MEANS FOR APPLYING SAID THIRD HYDRAULIC PRESSURE SIGNAL TO SAID ACTUATING MEANS, MEANS RESPONSIVE TO THE PRESSURE DROP ACROSS SAID BURNER FOR DEVELOPING A FOURTH HYDRAULIC PRESSURE SIGNAL, AND MEANS FOR APPLYING SAID FOURTH HYDRAULIC PRESSURE SIGNAL TO SAID ACTUATING MEANS, WHEREBY THE SAID ACTUATING MEANS WILL POSITION SAID FUEL REGULATING MEANS IN RESPONSE TO THE DIFFERENCE BETWEEN SAID THIRD HYDRAULIC PRESSURE SIGNAL AND SAID FOURTH HYDRAULIC PRESSURE SIGNAL. 